Fibrinogen is a plasma protein, synthesized in the liver, which in the final step of the blood coagulation cascade by activated thrombin is converted into insoluble fibrin. Fibrin in turn, is in the fibrinolysis reaction decomposed by plasmin, also referred to as fibrinolysin, the normal mechanism for the removal of small fibrin clots from the circulation.
The plasma fibrinogen concentration increases gradually during normal aging from an average of 2.3 mg/ml at 20 years to 3.5 mg/ml at 70 years of age. The increase is coupled with about a 20% decrease in endogenous fibrinolytic activity over the same period. Under conditions of stress or trauma the blood fibrinogen level may double or triple within 48 hours. It has been confirmed that blood fibrinogen is a major determinant of blood and plasma viscosity in the microcirculation, of red cell and platelet aggregation and in the growth of atheromatous lesions. Blood fibrinogen levels are increased and the endogenous fibrinolytic activity decreased by conditions or factors which raise plasma free fatty acid, FFA, levels, see Pickart, L., in Pharmacology 23: 271-280, 1981.
An increased level of fibrinogen is associated with an increased erythrocyte sedimentation rate, which in turn since long has been correlated to a risk for ischemic heart diseases. In acute myocardial infarction the level of plasma fibrinogen as well as the level of free fatty acids are increased.
Fibrinogen as a cardiovascular risk factor is described by Ernst, E., et al., Annals of Internal Medicine 118: 956-963, 1993. In six prospective epidemiologic studies the correlation of fibrinogen levels on the subsequent incidence of myocardial infarction, stroke and peripheral arterial occlusive disease was assessed and the causality of the association was analysed. All prospective studies showed that fibrinogen was associated with subsequent myocardial infarction or stroke. It was concluded that fibrinogen is pathophysiologically related to cardiovascular events and can be considered a major cardiovascular risk factor.
There are several determinants of the fibrinogen level in health and disease, some of which can not be affected such as age, sex and heritage. Others which are amenable to change are lifestyle determinants such as smoking, sedentary life, diet and stress.
An increased cholesterol level, as well as an increased blood pressure are other important risk factors for heart diseases. Serum cholesterol levels generally refer to a combination of HDL, high density lipoproteins, and LDL, low density lipoproteins. Increased levels of LDL cholesterol may be associated with the pathogenesis of atherosclerosis while higher levels of HDL cholesterol appear to lower the risk of heart disease.